Estetrol is a human steroid, produced by the fetal liver during pregnancy only. This natural hormone was discovered in urine of pregnant women by Diczfalusy and coworkers in 1965. Estetrol has the structure of an estrogenic steroid with four hydroxyl groups. Estetrol is synthesized in the fetal liver from estradiol and estriol by the two enzymes 15α- and 16α-hydroxylase. After birth the neonatal liver rapidly loses its capacity to synthesize estetrol because these two enzymes are no longer expressed.
Estetrol reaches the maternal circulation through the placenta and was already detected at nine weeks of pregnancy in maternal urine. During the second trimester of pregnancy high levels were found in maternal plasma, with steadily rising concentrations of unconjugated estetrol to about 1 ng/mL (>3 nmol/L) towards the end of pregnancy. So far the physiological function of estetrol is unknown. The possible use of estetrol as a marker for fetal well-being has been studied quite extensively. However, due to the large intra- and inter-individual variation of maternal estetrol plasma levels during pregnancy this appeared not to be feasible. Since 2001 estetrol has been studied extensively. In humans estetrol was shown to have a high and dose-proportional oral bioavailability and a long terminal elimination half-life of about 28 hours. Results from in vitro studies showed that estetrol binds highly selective to the estrogen receptors with preference for the ERa form of the receptor, unlike the estrogens ethinyl estradiol and 17β-estradiol. Also in contrast with ethinyl estradiol and especially with 17β-estradiol, estetrol does not bind to sex hormone binding globulin (SHBG) and does not stimulate the production of SHBG in vitro.
The properties of estetrol have also been investigated in a series of predictive, well validated pharmacological in vivo rat models. In these models, estetrol exhibited estrogenic effects on the vagina, the uterus (both myometrium and endometrium), body weight, bone mass, bone strength, hot flushes and on ovulation (inhibition). All these effects of estetrol were dose-dependent with maximum effects at comparable dose levels. Surprisingly, estetrol prevented tumour development in a DMBA mammary tumour model to an extent and at a dose level similar to the anti-estrogen tamoxifen and to ovariectomy. This anti-estrogenic effect of estetrol in the presence of 17β-estradiol has also been observed in in vitro studies using human breast cancer cells.
Buccal, sublingual or sublabial administration of estetrol is mentioned in a number of patent applications, including WO 2002/094275, WO 2002/094276, WO 2002/094278 and WO 2003/018026. Estetrol containing dosage units for buccal, sublingual or sublabial administration are not described in these publications.
WO 2010/033832 describes an oral dosage form comprising an estriol compound and a pharmaceutically acceptable matrix material, wherein the oral dosage form releases at least about 90% of the estriol compound in a time of less than about 300 seconds when contacted with saliva of the buccal and/or sublingual cavity.
US 2007/286829 describes an orally administered solid dosage form capable of delivering ethinyl estradiol with improved bioavailability, said solid dosage form comprising (i) about 0.5 μg to about 50 μg of ethinyl estradiol and (ii) an oral dissolution enhancing carrier that provides for at least 15% absorption of the ethinyl estradiol through the oral mucosa when said solid dosage form is orally administered to the patient with 2 ounces of water or less.
U.S. Pat. No. 6,117,446 describes a buccal dosage unit for administering a combination of steroidal active agents, comprising a compressed tablet of a bioerodible polymeric carrier and therapeutically effective amounts of an androgenic agent selected from testosterone and pharmacologically acceptable esters thereof, a progestin and an estrogen. The examples describe buccal dosage units that were prepared by thoroughly mixing the following components: estrogen, progestogen, androgen, polyethylene oxide, carbomer and magnesium stearate. Next, the mixture was granulated by means of fluid bed granulation and the granulate so obtained was pressed into tablets.
Oral dosage units containing estetrol have been described in several patent publications.
WO 2002/094276 describes a pharmaceutical composition for use in a method of hormone replacement therapy, which method comprises administering to a person in need of such a therapy an effective amount of estetrol, said composition containing virtually no progestogen or anti-progestin. WO 2002/094276 describes the preparation of estetrol tablets having a weight of 185 mg, containing 1.5 mg estetrol, on the basis of the following formulation:
mgEstetrol1.5Polyvinylpyrrolidone (Kollidon 25 ® ex12.5BASF)Lactose135.795Microcrystalline cellulose (Avicel PH 101 ®) 26.25Glyceryl palmitostearate (Precirol ®)2.775Anhydrous colloidal silica (Aerosil 200 ®)1.0Crospovidone (Polyplasdone XL ®)4.0Coloring agent0.18
WO 2002/094275 describes the use of an estetrol in a method of increasing libido in a woman, said method comprising administering to said woman an effective amount of estetrol. Oral administration is mentioned as a suitable mode of administration. This patent application describes the same estetrol tablet as WO 2002/094276.
WO 2002/094279 describes the use of estetrol in a method of contraception in mammalian females, which method comprises the oral administration of said estrogenic component and a progestogenic component to a female of childbearing capability in an effective amount to inhibit ovulation. The following formulation for a 185 mg estetrol tablet is described in this international patent application.
mgEstetrol1.5Levonorgestrel0.15Polyvinylpyrrolidone (Kollidon 25 ® ex13.5BASF)Lactose135.645Microcrystalline cellulose (Avicel PH 101 ®) 26.25Glyceryl palmitostearate (Precirol ®)2.775Anhydrous colloidal silica (Aerosil 200 ®)1.0Crospovidone (Polyplasdone XL ®)4.0Coloring agent0.18
WO 2003/041718 describes the use of estetrol in a method of hormone replacement in mammals, which method comprises the oral administration of estetrol and a progestogenic component to a mammal in an effective amount to prevent or treat symptoms of hypoestrogenism. This patent application describes the same estetrol tablet as WO 2002/094279.
WO 2007/081206 describes the use of estetrol in a method of treating an acute vascular disorder in a mammal, said method comprising orally administering to said mammal, upon demand, an effective amount of the estetrol to the mammal. This patent application describes the preparation of hard gelatine capsules, containing 100 mg estetrol and 25 mg sildenafil citrate per capsule. WO 2008/156365 describes the use of estetrol in the treatment of Meconium Aspiration Syndrome (MAS) in a newborn infant, said treatment comprising administering an effective amount of estrogen to said newborn infant within 7 days after birth. The international patent application describes a suppository for use in newborn infants comprising at least 1 μg of estrogen, said suppository further being characterized by a maximum diameter of less than 10 mm and a weight of less than 0.5 g. The excipient contained in the suppository may be based on lipid material that melts at body temperature or it may be based on a hydrophilic component that dissolves or disintegrates when it comes into contact with water.